Freezer with positive pressure storage cabinet

ABSTRACT

A freezer for the storage of blood plasma and other blood products is disclosed.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to refrigerators and freezers. More specifically, the present disclosure relates to freezers used in the storage of blood and blood products.

Freezers which operate at temperatures well below freezing such as those used in the storage and preservation of whole blood and other blood products, such as plasma, are accessed on a regular basis. In order to preserve the quality of the products stored in the equipment, the temperature within the storage cabinet must be controlled. The refrigerated compartment is accessed, for example, by opening the door. When the door is opened, ambient atmospheric air is introduced into the storage cabinet thereby increasing the temperature within the compartment. Moreover, moisture in the ambient air may condense in the storage cabinet, thereby reducing the effectiveness of the refrigeration process.

In some cases, the storage cabinet is maintained at a temperature well below freezing (0° C.), and even down to temperatures reaching −30° C. A freezer experiences repeated cycles of cooling of the air in the storage cabinet due to the storage cabinet being accessed to remove product. As most freezers are configured to be substantially air-tight when closed, the variation in temperature results in changes in the pressure within the storage cabinet according to the well known relationship of PV=nRT. The pressure gradient may result in ambient air being drawn into the storage cabinet through a seal. The ambient air contains moisture which freezes and results in localized frosting within the storage cabinet.

SUMMARY OF THE INVENTION

The present disclosure comprises one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter:

In one embodiment, a freezer comprises a cabinet having an external surface and defines an encloseable storage space within the cabinet. The cabinet also comprises an aperture or opening forming a fluid communication path between the storage space and the external surface. The freezer further comprises a door coupled to the cabinet and moveable between an open position and a closed position. In the closed position, the door encloses the storage space. The freezer still further comprises a chiller housed within the storage space, the chiller comprising refrigeration coils and a fan. The freezer yet still further comprises a positive pressure source coupled to an external surface of the cabinet, the positive pressure source having an inlet and an outlet wherein the positive pressure source receives ambient air in the inlet, pressurizes the air, and communicates the pressurized air through the aperture and into the storage space.

In some embodiments, the freezer may further comprise a conduit configured to be received in the aperture. When present the conduit may be coupled to the outlet of the positive pressure source and communicate the flow of pressurized air into the storage space. The conduit may direct the flow of air over the refrigeration coils. In some embodiments, the conduit may comprise a drain line of the freezer.

In another embodiment, an apparatus may comprise a freezer including an encloseable storage space and an aperture configured to permit fluid communication between the storage space and atmosphere. The apparatus may also comprise a positive pressure assembly configured to communicate ambient air through the aperture to induce a positive pressure in the storage space relative to atmosphere. In some embodiments, the freezer may comprise a door movable between an open position and a closed position wherein the storage space is enclosed.

In some embodiments, the positive pressure assembly may comprise a plenum and a positive pressure source coupled to the plenum. The plenum may include an outlet in fluid communication with the aperture. The positive pressure source may comprise a fan, a blower, or a compressor.

The apparatus may further comprise a conduit having an outlet, the conduit in fluid communication with the positive pressure assembly and configured to be received in the aperture of the freezer such that the outlet directs the air into the storage space. In some embodiments, the freezer may further comprise a chiller including refrigeration coils. The outlet of the conduit may be positioned to direct the flow of air over the refrigeration coils.

In some embodiments, the chiller may include a heating element configured to defrost the refrigeration coils. In still other embodiments, the conduit may comprise a drain line of the freezer. The drain line may include a heating element.

In some embodiments, the positive pressure assembly may develop a positive pressure within the storage space of about 0.25 inches of water above atmospheric pressure. The positive pressure assembly may be secured to the freezer.

A method of pressurizing a storage space of a freezer may include the steps of sealing the storage space within the freezer relative to ambient air, establishing a fluid communication path from a positive pressure source external to the freezer to the storage space in the freezer, positioning the positive pressure source to intake ambient air, and operating the positive pressure source to direct the air into the storage space and thereby develop a positive pressure within the storage space of the freezer relative to the ambient air. In some embodiments, the method may further include the step of directing the flow of pressurized air over a refrigeration coil within the storage space of the freezer. In other embodiments, the method may include the step of operating the positive pressure source continuously for a period of time. In some embodiments, the method may include the step of developing a static pressure within the storage space of the freezer

The present disclosure comprises one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter:

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figures in which:

FIG. 1 is a perspective view of a freezer with a door open exposing a storage space within a cabinet of the freezer;

FIG. 2 is a block diagram of the electrical system of the freezer of FIG. 1;

FIG. 3 is a back view of the freezer of FIG. 1 showing an exploded assembly of an embodiment of a positive pressure assembly; and

FIG. 4 is a back view of a portion of the freezer of FIG. 1 showing the plumbing of the positive pressure assembly of FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

A freezer 10 comprises a cabinet 12 which defines a storage space 14 configured to receive racks 16 and drawers 18 as shown in FIG. 1. Freezer 10 operates at a temperature of about (−30)° C. and is suitable for storing plasma or other blood products. Freezer 10 further comprises a door 20 which is pivotably coupled to cabinet 12 and is pivotable between an open position as shown in FIG. 1 and a closed position. When the door 20 is in the closed position, storage space 14 is covered and sealed such that storage space 14 is generally air-tight. This seals the storage space 14 relative to the ambient air in the atmosphere surrounding cabinet 12 of freezer 10. A chiller 22 operates to cool storage space 14 to the operating temperature and thereby cool blood products stored in storage space 14.

Freezer 10 further comprises a gasket 24 secured to door 20 and which engages a surface 26 about the perimeter of an opening 28 in cabinet 12. Opening 28 provides access to storage space 14 when door 20 is in an opened position. Gasket 24 comprises a flexible material and engages surface 26 when door 20 is closed. During engagement with surface 26, gasket 24 compresses under load and fills any irregularities between door 20 and surface 26 so as to generally seal storage space 14 relative to the ambient atmosphere. In the illustrative embodiment, gasket 24 comprises a polyvinyl chloride material. In other embodiments, any of a number of sealing materials may be utilized to seal storage space 14 when door 20 is in a closed position. Also, in some embodiments, gasket 24 may be positioned on cabinet 12 and may seal against a surface of door 20 when door 20 is in a closed position. Door 20 is held in a closed position by a latch 48 which has two apertures which are configured to receive two posts 52 on a handle assembly 54 coupled to door 20.

The operating temperature of about (−30)° C. of freezer 10 results in frosting within storage space 14. Freezer 10 may be used in a clinical or laboratory environment having an ambient temperature of about 21-23° C. and about 50% relative humidity. Thus, when door 20 is opened, relatively warm and moist air is introduced into storage space 14. Moisture in the ambient air condenses in the relative cold storage space 14 and freezes creating frost which attaches to structures within storage space 14. The nature of the operation of freezer 10 further exacerbates the frosting problem. For example, when door 20 is closed, storage space 14 becomes a generally closed volume. The well known equation PV=RT models the volume. Generally, pressure (P), volume (V) and temperature (T) are interdependent variables. When door 20 is closed, volume (V) becomes constant. Thus, pressure (P) is dependent upon temperature (T). Chiller 22 operates intermittently to maintain the temperature within storage space 14 at a target temperature. Every time chiller 22 operates, temperature (T) is lowered slightly. As discussed above, pressure (P) is directly related to temperature (T) in a closed volume and, therefore, a slight reduction in temperature (T) results in a proportional reduction in pressure (P).

When door 20 is first closed, the pressure within storage space 14 approximates the ambient air pressure outside of freezer 10. However, lowering of the temperature within storage space 14 results in a lower pressure within storage space 14 as well. It has been found that in operation the pressure within storage space 14 may be lowered by as much as about 0.25 inches of water to even about 0.50 inches of water below the ambient pressure outside of freezer 10. If gasket 24 does not completely seal storage space 14 from the ambient atmosphere outside of cabinet 12, then as the system attempts to reach equilibrium, ambient air flows through the unsealed portion of gasket 24. This ambient air includes moisture which condenses and freezes near the unsealed portion of gasket 24. Every time chiller 22 operates, the temperature (T) within storage space 14 is lowered slightly and thereby pressure (P) is lowered creating a pressure gradient between storage space 14 and ambient air. Thus, frost continues to form around areas in which gasket 24 does not completely seal storage space 14 from ambient.

Frost within storage space 14 is removed automatically by regular defrost cycles within freezer 10. More specifically, freezer 10 operates under the control of a controller 110, shown diagrammatically in FIG. 2, and is operable to chill storage space 14. Chiller 22 is a compressor-based unit with a fan 30 (see FIG. 1) and coils 32. Referring again to FIG. 2, a coil heater 138 is operable to defrost coils 32. It is necessary to defrost coils 32 so that the operation of freezer 10 is efficient and predictable. If frost is maintained on coils 32 the heat transfer rate to coils 32 is diminished. Thus, chiller 22 may not chill storage space 14 as efficiently or quickly as under normal operating conditions. The chiller 22 is controlled by controller 110 based on the expected performance of coils 32. Defrosting of coils 32 and other components of freezer 10 maintains the expected performance by preventing the insulating effect of frost on coils 32 and other portions of freezer 10.

As shown in FIG. 1, freezer 10 further includes a monitor unit 200 which includes a user interface device 34. User interface device 34 has a display 36 and multiple input devices 38. Monitor unit 200 is in communication with controller 110 to provide input to controller 110 from a user through the input devices 38 of the user interface device 34. Monitor unit 200 also provides visual output to the user via the display 36. A user is able to (i) set a target operating temperature, (ii) set defrost trigger parameters and timing, and (iii) monitor performance of freezer 10 through user interface device 34.

Additionally, monitor unit 200 is coupled to a battery 114, shown in FIG. 2, which provides power to monitor unit 200 in case of a power loss. The battery 114 is sized sufficiently to provide power to stabilize volatile memory 116 within monitor unit 200 and to continue to maintain a real time clock in monitor unit 200. In this way, in the event of a power loss monitor unit 200 maintains operating parameters programmed by a user in memory. Further, memory 116 stores operational data related to defrost cycles, the number of times door 20 is opened, and temperature data. In the illustrative embodiment, monitor unit 200 has an independent temperature sensor 144 and does not gather information from temperature sensor 44. In other embodiments, monitor unit 200 may acquire temperature data from temperature sensor 44 and temperature sensor 144 may be omitted. In still other embodiments, monitor unit 200 may acquire temperature data from temperature sensors 44 and 144 or even additional temperature sensors. This information is viewable on display 36 and may be accessed through an external connector 122 to be downloaded to a separate computer (not shown), such as a laptop computer. In the illustrative embodiment, data is accessed through connector 122 using an RS232 serial communications protocol. In other embodiments, any of a number of protocols may be used to access the data.

The interaction of controller 10 and the various input and output devices is shown diagrammatically in FIG. 2. Controller 110 is in communication with monitor unit 200 and various other peripheral devices to either receive inputs or provide outputs. Controller 110 receives power from a power supply 112 which is coupled to a main power source 126. The main power source 126 is a 110 volt AC power source as is typically found in wall outlets. In some embodiments, the main power source 126 may be a 230 volt AC power source. The power supply 112 includes transformers, conditioners, and filters to provide the correct voltage and current to various equipment coupled to the power supply 112.

Controller 110 is also in communication with chiller 22 and operable to turn chiller 22 on and off. A defrost system 118 includes resistive coils which provide heat when powered. Controller 110 is configured to activate defrost system 118 as necessary. Defrost system 118 powers the resistive coils so that frost which has accumulated may be melted. By providing localized heating, the frost is melted relatively quickly without introducing excessive heat to the storage space 14.

Coil heater 138, embodied as a resistive heating element, is part of defrost system 118 and is located adjacent to coils 32 of chiller 22 and operable to defrost coils 32. A door heater 134 is coupled to door 20 and operable to defrost the inside of door 20. Yet another heater, a drain line heater 136, is coupled to a drain line 40 (best seen in FIG. 4). Drain line 40 is coupled to a drip tray 42 in storage space 14 and receives fluid that results from the melting of frost, the fluid is urged by gravity through drain line 40 and out of the storage space 14 into an evaporator tray 60 secured to a back surface 46 of cabinet 12. A drip tray heater 132 is coupled to a drip tray 42 (seen in phantom in FIG. 4). Drip tray 42 captures the fluid that results from melting frost and drip tray heater 132 heats the fluid so that it may enter drain line 40. In some embodiments, drip tray heater 132 may be omitted and coil heater 138 (see FIG. 2) may be extended to heat drip tray 42. The fluid from drain line 40 accumulates into evaporator tray 60. An evaporator coil 140 is another resistive coil which operates to evaporate the fluid accumulated in evaporator tray 60. The evaporator coil 140 is independent from defrost system 118 and may be selectively activated by controller 110. In some embodiments, evaporator coil 140 may be coupled directly to power supply 112 and operate continuously. In operation, the defrost system 118 melts excess frost and assures that excess moisture is removed from storage space 14. In some embodiments, one or more of the drip tray heater 132, door heater 134, or drain line heater 136 may be omitted. In some embodiments, one or more of the drip tray heater 132, door heater 134, or drain line heater 136 may be coupled directly to the power supply 112 and operate continuously.

Controller 110 also communicates with a temperature sensor 44 to receive a signal from the temperature sensor 44, the signal being indicative of the temperature within the storage space 14. Controller 110 processes the temperature signal to control chiller 22 and monitor for the need to defrost. Additionally, controller 110 receives a signal from a door switch 120 which provides an indication that door 20 is closed. Door switch 120 is located on cabinet 12 and is activated when door 20 is closed. Controller 110 has an interlock which, in normal operation, requires door 20 to be closed before activating defrost system 118.

Referring again now to FIGS. 3 and 4, freezer 10 includes a positive pressure assembly 56 mounted on the back surface 46 of cabinet 12. The positive pressure assembly 56 comprises a positive pressure source 58 coupled to a plenum 62. A cover 64 is coupled to positive pressure source 58. Four fasteners 80 are received in holes 82 formed in plenum 62 and retain plenum 62, positive pressure source 58 and cover 64 together to form positive pressure assembly 56. Positive pressure source 58 is electrically connected to controller 110 and power supply 112 as shown in FIG. 2. In the illustrative embodiment, positive pressure source 58 is a fan model number UF80B23-BWH from Mechatronics®, Inc. In other embodiments, any of a number of devices may be used to provide a source of positive pressure. For example, blowers and compressors produce positive pressure and may used as a positive pressure source.

Plenum 62 includes an outlet 66 which provides a path for fluid to flow out of plenum 62. A conduit 68 is coupled to plenum 62 in fluid communication with outlet 66. Conduit 68 is coupled to drain line 40 through a connector 70 and is thereby in fluid communication with drain line 40. Drain line 40 communicates through back surface 46 of cabinet 12 to drip tray 42 such that fluid accumulated in drip tray 42 is urged by gravity to flow into drain line 40. Drain line 40 is j-shaped and includes a lower portion 72 positioned above evaporator tray 60. An end 76 of drain line 40 is configured to allow fluid to escape through end 76 into evaporator tray 60.

The structure of drain line 40 is such that pressurized air from positive pressure source 58 is limited to flow through drain tube 40 through fluid in drip tray 42 and into storage space 14. Fluid accumulates in the lower portion 72 of drain line 40 so as to create a barrier to the escape of pressurized air through end 76 of drain line 40. The pressure developed by pressure source 58 is not sufficient to expel the fluid from drain line 40 and therefore, the fluid acts as a seal and pressurized air is directed into storage space 14.

The flow of pressurized air into storage space 14 tends to pressurize storage space 14 at a pressure higher than atmosphere. Pressurization of storage space 14 results in the reduction and near elimination of flow of ambient air into storage space 14. Storage space 14 is at a higher pressure than atmosphere and therefore air from storage space 14 tends to be urged to escape any areas in which gasket 24 does not completely seal storage space 14 from ambient This reduces the potential for ingress of ambient air and the subsequent development of frost near gasket 24.

Positive pressure source 58 draws in ambient air from around freezer 10 as shown by the arrows in FIG. 3. As described above, the ambient air contains moisture which condenses into frost when introduced into storage space 14. Drain line 40 is a conduit with an inlet 78 at drip tray 42. Inlet 78 functions as the outlet for the flow of pressurized air into storage space 14. The position of inlet 78 results in the flow of pressurized ambient air to be directed over coils 32 of chiller 22. Moisture in the ambient air is condensed onto coils 32. This results in localized frosting on coils 32 which is addressed by defrost system 118 and specifically coil heater 138 when freezer 10 is in a defrost mode. Frost is removed by coil heater 138 as part of the operation of freezer 10 as described above.

Positive pressure assembly 56 operates such that after a maximum pressure head is developed within storage space 14, losses within positive pressure assembly 56 prevent additional pressure from being developed within storage space 14 and there is little or no flow from positive pressure assembly 56. This results in limiting the amount of ambient air introduced into storage space 14 and limits the amount of frost developed on coils 32. In the illustrative embodiments, positive pressure assembly 56 is sized such that the pressure developed within storage space 14 is about 0.25 inches of water above atmosphere. It has been found that 0.25 inches of water provides an appropriate pressurization to limit frosting near gasket 24 as well as on coils 32.

While the illustrative embodiment utilizes drain line 40 as a conduit for the flow of air from positive pressure assembly 56, it should be understood that a positive pressure source 58 may communicate through any of a number of conduits or apertures. For example, in some embodiments a conduit dedicated to the flow of pressurized air into storage space 14 may be utilized. In other embodiments, the conduit may be omitted and positive pressure source 58 may be in fluid communication with an aperture in cabinet 12 such that air flows directly from positive pressure source 58 into storage space 14.

In some embodiments, the flow of ambient air into storage space 14 may be directed to structures other than coils 32 to control the development of frost. For example, in some embodiments ambient air may be directed over a removable structure in storage space 14. The removable structure may then be removed so that frost can be removed from the structure external to freezer 10.

In the illustrative embodiment, positive pressure source 58 operates continuously. In other embodiments, controller 110 may selectively operate positive pressure source 58 based on other conditions of operation of freezer 10. For example, positive pressure source 58 may be turned off whenever door 20 is opened.

Although certain illustrative embodiments have been described in detail above, variations and modifications exist within the scope and spirit of this disclosure as described and as defined in the following claims. 

1. An apparatus comprising, a freezer comprising an encloseable storage space and an aperture configured to permit fluid communication between the storage space and atmosphere, and a positive pressure assembly configured to communicate ambient air through the aperture to induce a positive pressure in the storage space relative to atmosphere.
 2. The apparatus of claim 1, wherein the freezer further comprises a door movable between an open position and a closed position enclosing the storage space.
 3. The apparatus of claim 1, wherein the positive pressure assembly comprises a plenum and a positive pressure source coupled to the plenum.
 4. The apparatus of claim 3, wherein the plenum includes an outlet in fluid communication with the aperture.
 5. The apparatus of claim 4, wherein the positive pressure source comprises a device selected from the group of a fan, a blower, or a compressor.
 6. The apparatus of claim 1, further comprising a conduit having an outlet, the conduit in fluid communication with the positive pressure assembly and configured to be received in the aperture of the freezer such that the outlet directs the ambient air into the storage space.
 7. The apparatus of claim 6, wherein the freezer further comprises a chiller including refrigeration coils and the outlet of the conduit is positioned to direct flow over the refrigeration coils.
 8. The apparatus of claim 7, wherein the chiller includes a heating element configured to defrost the refrigeration coils.
 9. The apparatus of claim 8, wherein the conduit comprises a drain line of the freezer.
 10. The apparatus of claim 9, wherein the drain line includes a heating element.
 11. The apparatus of claim 1, wherein the positive pressure assembly develops a pressure within the storage space of about 0.25 inches of water above atmospheric pressure.
 12. The apparatus of claim 1, wherein the positive pressure assembly is secured to the freezer.
 13. A method of pressurizing a storage space of a refrigerator comprising: sealing the storage space within the freezer relative to ambient air, establishing a fluid communication path from a positive pressure source external to the freezer to the storage space in the freezer, positioning the positive pressure source to intake ambient air, and operating the positive pressure source to direct the air into the storage space and thereby develop a positive pressure within the storage space of the freezer relative to the ambient air.
 14. The method of claim 13 further comprising the step of directing the flow of pressurized air over a refrigeration coil within the storage space of the freezer.
 15. The method of claim 13 further comprising the step of operating the positive pressure source continuously.
 16. The method of claim 15 further comprising the step of developing a static pressure within the storage space of the freezer.
 17. A freezer comprising, a cabinet having an external surface and defining an encloseable storage space therein and an aperture forming a fluid communication path between the storage space and the external surface, a door coupled to the cabinet and moveable between an open position and a closed position, wherein the storage space is enclosed when the door is in the closed position, a chiller comprising refrigeration coils and a fan, the chiller housed within the storage space, and a positive pressure source coupled to an external surface of the cabinet, the positive pressure source having an inlet and an outlet, wherein the positive pressure source receives ambient air in the inlet, pressurizes the air, and communicates the pressurized air through the aperture and into the storage space.
 18. The freezer of claim 17, further comprising a conduit configured to be received in the aperture, the conduit coupled to the outlet of the positive pressure source and communicating the flow of pressurized air into the storage space.
 19. The freezer of claim 18, wherein the conduit directs the flow of fluid over the refrigeration coils.
 20. The freezer of claim 19, wherein the conduit comprises a drain line of the freezer. 